Material for forming insulating film with low dielectric constant, low dielectric insulating film, method for forming low dielectric insulating film and semiconductor device

ABSTRACT

A material for forming an insulating film with low dielectric constant of this invention is a solution including a fine particle principally composed of a silicon atom and an oxygen atom and having a large number of pores, a resin and a solvent.

BACKGROUND OF THE INVENTION

The present invention relates to a material for forming an insulatingfilm with low dielectric constant, an insulating film with lowdielectric constant, a method for forming an insulating film with lowdielectric constant and a semiconductor device including an insulatingfilm with low dielectric constant.

Recently, a multilayer interconnect structure including an insulatingfilm with low dielectric constant is necessary for realizing refinement,a high-speed operation and a low power consuming operation of asemiconductor device.

A conventional insulating film used in a multilayer interconnectstructure is, for example, a silicon oxide film having a dielectricconstant of approximately 4.2 or a silicon oxide film doped withfluorine having a dielectric constant of approximately 3.7. Also, inorder to further lower the low dielectric constant, an organiccomponent-containing silicon oxide film doped with a methyl group (CHF₃)is recently under examination.

It is, however, very difficult to lower the dielectric constant of anorganic component-containing silicon oxide film below 2.5, andtherefore, an insulating film having pores, namely, what is called aporous film, is necessary.

Now, conventional technique for a porous film will be described.

First, a first conventional example and a second conventional exampledisclosed in Japanese Laid-Open Patent Publication No. 2001-294815 willbe described.

In the first conventional example, a porous film is formed by baking athin film made from a solution including a silicon resin and an organicsolvent. In this example, open pores are randomly formed in portionswhere the organic solvent has been vaporized in baking the thin film. Inthis case, the organic solvent has a function as a solvent as well as afunction to form the pores. In general, a spin coating method isemployed for forming the thin film by applying the solution on asubstrate, and a hot plate and a furnace (electric furnace) are used forbaking the thin film.

In the second example, a porous film is formed by baking a thin filmmade from a solution including not only a silicon resin and an organicsolvent but also a porogen of an organic substance. In this example, notonly open pores but also closed pores can be formed through selection ofthe porogen. In this case, the porogen is naturally vaporized todisappear from the resultant film.

Next, a third conventional example disclosed in Japanese Laid-OpenPatent Publication No. 8-181133 will be described.

A porous film of the third conventional example has conceptually themost general structure and is formed by using a solution as shown inFIG. 9. Specifically, as shown in FIG. 9, a solution in which a siliconresin 102, a porogen 103 and a solvent 104 are mixed is contained in avessel 101.

In the third conventional example, which is disclosed in JapaneseLaid-Open Patent Publication No. 8-181133, a porous film is formed bybaking a thin film made from a solution including a fullerene such asC60 or C70, a silicon resin and an organic solvent. In this case, ahollow portion of the fullerene becomes a pore of the porous film.

As the silicon resin used in the first, second and third conventionalexamples, an organic silicon resin such as methylsilsesquioxane capableof lowering the dielectric constant as compared with an inorganicsilicon resin is used.

Now, an exemplified conventional method for forming a thin film from asolution will be described with reference to FIGS. 10A through 10F. Ingeneral, a substrate on which a thin film has been formed by the spincoating method is baked with a hot plate or an electric furnace.

First, as shown in FIG. 10A, a semiconductor wafer 112 is placed on aspindle 111 connected to a rotation mechanism, and thereafter, anappropriate amount of solution 114 used for forming a porous film isdropped on the semiconductor wafer 112 from a solution supply tube 113.

Next, as shown in FIG. 10B, the spindle 111 is rotated so as to rotatethe semiconductor wafer 112, and thus, the solution 114 is spread so asto form a thin film 115.

Then, as shown in FIG. 10C, the semiconductor wafer 112 on which thethin film 115 has been formed is placed on and annealed with a hot plate116 so as to vaporize the solvent. This procedure is generallydesignated as pre-bake and is performed at a temperature ofapproximately 100° C. for approximately 1 through 3 minutes.

Next, as shown in FIG. 10D, the semiconductor wafer 112 is placed on ahot plate 117 to be annealed at a temperature of approximately 200° C.for 1 through 3 minutes. This procedure is generally designated as softbake.

Thereafter, as shown in FIG. 10E, the resultant semiconductor wafer 112is placed in an electric furnace 118, and then, the temperature of theelectric furnace 118 is increased to approximately 400° C. through 450°C., so that annealing can be performed at the highest set temperaturefor approximately 1 hour. This procedure is generally designated as hardbake, and when this procedure is completed, a porous film 115A is formedon the semiconductor wafer 112. The hard bake can be performed by usinga hot plate. Also, in using some solution, annealing is preferablyperformed, between the soft bake and the hard bake, with a hot plate atan intermediate temperature between the temperatures of the soft bakeand the hard bake for approximately 1 through 3 minutes.

FIG. 10F is an enlarged view of a portion surrounded with an alternatelong and short dash line in FIG. 10E. As is understood from FIG. 10F,pores 119 (white portions in the drawing) are formed in the porous film115A formed on the semiconductor wafer 112.

The mechanical strength of the porous film 115A obtained throughnano-indentation evaluation is at most approximately 5 GPa in theYoung's modulus. With respect to insulating films that are currentlyactually used in semiconductor devices, the modulus of a silicon oxidefilm is approximately 78 GPa, the modulus of a fluorine-containingsilicon oxide film is approximately 63 GPa and the modulus of an organiccomponent-containing silicon oxide film is approximately 10 GPa. Thus,the mechanical strength of the porous film 115A is smaller than that ofany other insulating film used in a multilayer interconnect structure ofa current semiconductor device, and accordingly, a porous film withlarger mechanical strength is desired to be developed.

FIG. 11 shows the cross-sectional structure obtained in bonding a wireto a semiconductor device that has a three-layer interconnect structureand uses a conventional porous film as an insulating film. In FIG. 11, areference numeral 120 denotes a semiconductor wafer, a reference numeral121 denotes a porous film, reference numerals 122, 124 and 126 denotemetal interconnects, reference numerals 123, 125, 126 and 128 denote viaplugs and a reference numeral 129 denotes a pad to be connected to anexternal interconnect.

As shown in FIG. 11, when a wire 130 is bonded to the upper face of thepad 129, a crack is caused in the pad 129 and the multilayerinterconnects.

The mechanical strength of the porous film 115A is necessary forretaining multilayered interconnects stacked for forming a multilayerstructure as well as in bonding for mounting a chip of a semiconductordevice in a package as described above. In the case where an organiccomponent-containing silicon oxide film is used as an insulating film,the mechanical strength is at a level of the very limit of breakdownobtained in employing the current bonding technique, and although thebonding technique is expected to be further developed in the future,development of a porous film with large mechanical strength is of urgentnecessity.

In the first and second conventional examples, the open pores arerandomly formed. Therefore, in order to realize an insulating film witha dielectric constant k of 2.2 through 2.3, the Young's modulus ofapproximately 5 GPa or less in the nano-indentation evaluation can beattained at most. This mechanical strength depends upon the method forforming the film in the first or second example. Specifically, theporogen and the solvent are not present but the silicon resin alone ispresent in the porous film after the bake, and therefore, the mechanicalstrength of the porous film depends upon the original strength of thesilicon resin and the porosity (a ratio occupied by pores in a unitvolume). In the first or second conventional example, when thedielectric constant is to be further lowered, the porosity is increased,which further lowers the mechanical strength.

In the third conventional example, although the fullerene remains in theporous film after the bake, the mechanical strength basically dependsupon the strength of the silicon resin including the fullerene and henceis at the same level as that attained in the first or secondconventional example. Also, when the content of the fullerene exceedsapproximately 30 wt %, the fullerenes are connected to each other, andtherefore, the mechanical strength is further lowered.

As described so far, a practically usable rigid film cannot be obtainedby any of the conventional methods for forming a porous film becausethere is a limit in the mechanical strength of the structure itself ofthe porous film of a silicon resin.

Also, a conventional porous film can attain merely mechanical strengthmuch lower than the mechanical strength necessary for a semiconductordevice, and when the dielectric constant of the porous film is to belowered, the mechanical strength is disadvantageously lowered.

As a result, in the case where a conventional porous film is actuallyused in a multilayer interconnect structure of a semiconductor device,there arise a problem that a semiconductor device with sufficientstrength cannot be fabricated and a problem that even when asemiconductor chip can be fabricated, the semiconductor device cannot becompleted because it is broken in mounting the chip in a package.

SUMMARY OF THE INVENTION

In consideration of the aforementioned conventional problems, an objectof the invention is increasing the mechanical strength of an insulatingfilm with low dielectric constant made of a porous film.

In order to achieve the object, the first material for forming aninsulating film with low dielectric constant of this invention includesa solution containing a fine particle that is principally composed of asilicon atom and an oxygen atom and has a large number of pores; aresin; and a solvent.

In using the first material for forming an insulating film with lowdielectric constant, an insulating film having a low dielectric constantand large mechanical strength can be easily and definitely formed.

In the first material for forming an insulating film with low dielectricconstant, the fine particle preferably has a size more thanapproximately 1 nm and less than approximately 30 nm.

Thus, when the resultant low dielectric insulating film is providedbetween metal interconnects, an interconnect groove with a goodcross-sectional shape can be formed in the low dielectric insulatingfilm if the metal interconnects are buried interconnects, and a smoothinsulating film free from a gap can be formed if the metal interconnectsare patterned interconnects.

In the first material for forming an insulating film with low dielectricconstant, each of the pores in the fine particle preferably has a sizemore than approximately 0.5 nm and less than approximately 3 nm.

Thus, a large number of pores can be definitely formed within the fineparticle.

In the first material for forming an insulating film with low dielectricconstant, the pores in the fine particle may be partially confined orisolated.

In the first material for forming an insulating film with low dielectricconstant, the fine particle is preferably formed by mechanicallycrushing a substance having a plurality of open pores randomlydistributed.

Thus, the fine particle having a large number of open pores can bedefinitely obtained.

In the first material for forming an insulating film with low dielectricconstant, the fine particle is preferably formed by mechanicallycrushing a substance having a large number of closed pores substantiallyuniformly dispersed.

Thus, the fine particle having a large number of closed pores can bedefinitely obtained.

In the first material for forming an insulating film with low dielectricconstant, the fine particle is preferably synthesized through a chemicalreaction.

Thus, the fine particle with a uniform size can be definitely obtained.

In the first material for forming an insulating film with low dielectricconstant, the resin is preferably a silicon resin.

Thus, the mechanical strength of the resultant low dielectric insulatingfilm can be further increased.

In this case, the silicon resin preferably includes organic silicon.

Thus, the mechanical strength can be increased as well as the dielectricconstant can be lowered in the resultant low dielectric insulating film.

In the first material for forming an insulating film with low dielectricconstant, the resin is preferably an organic polymer.

Thus, the dielectric constant of the resultant low dielectric insulatingfilm can be further lowered.

In the first material for forming an insulating film with low dielectricconstant, the solution preferably further includes a compound forreinforcing bond between the resin and the fine particle.

Thus, the mechanical strength of the resultant low dielectric insulatingfilm can be further increased.

The second material for forming an insulating film with low dielectricconstant of this invention includes a fine particle, and the fineparticle is formed by mechanically crushing a substance that isprincipally composed of a silicon atom and an oxygen atom and has aplurality of open pores randomly distributed, and the fine particle hasa large number of pores formed by the plurality of open pores.

In using the second material for forming an insulating film with lowdielectric constant, an insulating film having a low dielectric constantand large mechanical strength can be formed. In this case, conditions inthe temperature, the pressure and the fabrication atmosphere, which arerestricted in using a conventional porous film, are not restricted inthe fabrication process for a semiconductor device. Therefore, thedegree of freedom in producing the substance having randomly distributedopen pores is increased, so that a fine particle with large mechanicalstrength can be obtained.

The third material for forming an insulating film with low dielectricconstant of this invention includes a fine particle, and the fineparticle is formed by mechanically crushing a substance that isprincipally composed of a silicon atom and an oxygen atom and has alarge number of closed pores substantially uniformly dispersed, and thefine particle has a large number of pores formed by the closed pores.

In using the third material for forming an insulating film with lowdielectric constant, an insulating film having a low dielectric constantand large mechanical strength can be formed. In this case, conditions inthe temperature, the pressure and the fabrication atmosphere, which arerestricted in using a conventional porous film, are not restricted inthe fabrication process for a semiconductor device. Therefore, thedegree of freedom in producing the substance having substantiallyuniformly dispersed closed pores is increased, so that a fine particlewith large mechanical strength can be obtained.

The fourth material for forming an insulating film with low dielectricconstant of this invention includes a fine particle, and the fineparticle is synthesized through a chemical reaction, is principallycomposed of a silicon atom and an oxygen atom and has a large number ofpores.

In using the fourth material for forming an insulating film with lowdielectric constant, an insulating film having a low dielectric constantand large mechanical strength can be formed. In this case, conditions inthe temperature, the pressure and the fabrication atmosphere, which arerestricted in using a conventional porous film, are not restricted inthe fabrication process for a semiconductor device. Therefore, thedegree of freedom in producing a substance having a large number ofpores is increased, so that a fine particle with large mechanicalstrength can be obtained.

The method for forming an insulating film with low dielectric constantof this invention includes the steps of forming a thin film by applying,on a substrate, a solution including a fine particle principallycomposed of a silicon atom and an oxygen atom and having a large numberof pores, a resin and a solvent; and annealing the substrate forevaporating the solvent, whereby forming an insulating film with lowdielectric constant out of the thin film.

In the method for forming an insulating film with low dielectricconstant of this invention, the low dielectric insulating film is formedby evaporating the solvent from the thin film made from the solutionincluding the fine particle, the resin and the solvent by annealing thesubstrate. Therefore, the low dielectric insulating film has a structurein which the fine particle having a large number of pores is introducedinto a structure of the resin and hence attains a low dielectricconstant and large mechanical strength. Also, when the ratio of the fineparticle in the solution is increased, the dielectric constant can belowered without lowering the mechanical strength.

In the method for forming an insulating film with low dielectricconstant, the fine particle preferably has a size more thanapproximately 1 nm and less than approximately 30 nm.

Thus, when the resultant low dielectric insulating film is providedbetween metal interconnects, an interconnect groove with a goodcross-sectional shape can be formed in the low dielectric insulatingfilm if the metal interconnects are buried interconnects, and a smoothinsulating film free from a gap can be formed if the metal interconnectsare patterned interconnects.

In the method for forming an insulating film with low dielectricconstant, each of the pores in the fine particle preferably has a sizemore than approximately 0.5 nm and less than approximately 3 nm.

Thus, a large number of pores can be definitely formed within the fineparticle.

In the method for forming an insulating film with low dielectricconstant, the resin is preferably a silicon resin.

Thus, the mechanical strength of the resultant low dielectric insulatingfilm can be further increased.

In this case, the silicon resin preferably includes organic silicon.

Thus, the mechanical strength can be increased as well as the dielectricconstant can be lowered in the resultant low dielectric insulating film.

In the method for forming an insulating film with low dielectricconstant, the resin is preferably an organic polymer.

Thus, the dielectric constant of the resultant low dielectric insulatingfilm can be further lowered.

In the method for forming an insulating film with low dielectricconstant, the solution preferably further includes a compound forreinforcing bond between the resin and the fine particle.

Thus, the mechanical strength of the resultant low dielectric insulatingfilm can be further increased.

In the method for forming an insulating film with low dielectricconstant, the step of annealing the substrate preferably includes asub-step of bonding the fine particle to the resin.

Thus, the mechanical strength of the low dielectric insulating film canbe further increased.

The low dielectric insulating film of this invention includes a fineparticle principally composed of a silicon atom and an oxygen atom andhaving a large number of pores; and a resin bonded to the fine particle.

Since the low dielectric insulating film of this invention has astructure in which the resin and the fine particle having a large numberof pores are bonded to each other, it attains a low dielectric constantand large mechanical strength.

In the low dielectric insulating film, the fine particle preferably hasa size more than approximately 1 nm and less than approximately 30 nm.Thus, when the low dielectric insulating film is provided between metalinterconnects, an interconnect groove with a good cross-sectional shapecan be formed in the low dielectric insulating film if the metalinterconnects are buried interconnects, and a smooth insulating filmfree from a gap can be formed if the metal interconnects are patternedinterconnects.

In the low dielectric insulating film, each of the pores in the fineparticle preferably has a size more than approximately 0.5 nm and lessthan approximately 3 nm.

Thus, a large number of pores can be definitely formed within the fineparticle.

In the low dielectric insulating film, the resin is preferably a siliconresin.

Thus, the mechanical strength of the low dielectric insulating film canbe further increased.

In this case, the silicon resin preferably includes organic silicon.

Thus, the mechanical strength can be increased as well as the dielectricconstant can be lowered in the low dielectric insulating film.

In the low dielectric insulating film, the resin is preferably anorganic polymer.

Thus, the dielectric constant of the low dielectric insulating film canbe further lowered.

In the low dielectric insulating film, the solution preferably furtherincludes a compound for reinforcing bond between the resin and the fineparticle.

Thus, the mechanical strength of the low dielectric insulating film canbe further increased.

The semiconductor device of this invention includes a plurality of metalinterconnects; and an insulating film with low dielectric constantformed between the plurality of metal interconnects, and the lowdielectric insulating film includes a fine particle principally composedof a silicon atom and an oxygen atom and having a large number of pores,and a resin bonded to the fine particle. The plural metal interconnectsherein may be a lower metal interconnect and an upper metal interconnector adjacent metal interconnects formed in one interconnect layer.

In the semiconductor device of this invention, even when the dielectricconstant of the low dielectric insulating film is lowered, itsmechanical strength is large, and therefore, cracks can be preventedfrom being caused in the metal interconnects.

In the semiconductor device, the fine particle preferably has a sizemore than approximately 1 nm and less than approximately 30 nm.

Thus, an interconnect groove with a good cross-sectional shape can beformed in the low dielectric insulating film if the metal interconnectsare buried interconnects, and a smooth insulating film free from a gapcan be formed if the metal interconnects are patterned interconnects.

In the semiconductor device, each of the pores in the fine particlepreferably has a size more than approximately 0.5 nm and less thanapproximately 3 nm.

Thus, a large number of pores can be definitely formed within the fineparticle.

In the semiconductor device, the resin is preferably a silicon resin.

Thus, the mechanical strength of the low dielectric insulating film canbe further increased.

In this case, the silicon resin preferably includes organic silicon.

Thus, the mechanical strength can be increased as well as the dielectricconstant can be lowered in the low dielectric insulating film.

In the semiconductor device, the resin is preferably an organic polymer.

Thus, the dielectric constant of the low dielectric insulating film canbe further lowered.

In the semiconductor device, the low dielectric insulating filmpreferably further includes a compound for reinforcing bond between theresin and the fine particle.

Thus, the mechanical strength of the low dielectric insulating film canbe further increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a solution that is a material forforming an insulating film with low dielectric constant according toEmbodiment 1 of the invention;

FIGS. 2A and 2B are cross-sectional views of a fine particle of amaterial for forming an insulating film with low dielectric constantaccording to Embodiment 2 of the invention;

FIGS. 3A and 3B are cross-sectional views of a fine particle of amaterial for forming an insulating film with low dielectric constantaccording to Embodiment 3 of the invention;

FIGS. 4A, 4B and 4C are cross-sectional views of fine particles of amaterial for forming an insulating film with low dielectric constantaccording to Embodiment 4 of the invention;

FIGS. 5A, 5B, 5C, 5D and 5E are cross-sectional views for showingprocedures in a method for forming an insulating film with lowdielectric constant according to Embodiment 5 of the invention;

FIGS. 6A and 6B are cross-sectional views of low dielectric insulatingfilms according to Embodiment 6 of the invention;

FIGS. 7A and 7B are cross-sectional views of the low dielectricinsulating film according to Embodiment 6 of the invention;

FIG. 8 is a cross-sectional view of a semiconductor device according toEmbodiment 7 of the invention;

FIG. 9 is a conceptual diagram of a solution used for forming aconventional porous film;

FIGS. 10A, 10B, 10C, 10D, 10E and 10F are cross-sectional views forshowing procedures in a method for forming a conventional porous film;and

FIG. 11 is a cross-sectional view for explaining a problem occurring ina semiconductor device using the conventional porous film.

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1

Embodiment 1 of the invention will now be described with reference toFIG. 1. In Embodiment 1, a material for forming an insulating film withlow dielectric constant is embodied as a solution.

As shown in FIG. 1, the solution according to Embodiment 1 is containedin a vessel 1, and includes a silicon resin 2 corresponding to a resin,fine particles 3 each having a large number of pores and a solvent 4.

As the silicon resin 2, inorganic silicon, organic silicon or a mixtureof them can be used. When organic silicon is used, the dielectricconstant of a resultant low dielectric insulating film can be furtherlowered.

The fine particles 3 having a large number of pores are made from acompound principally formed through bonding between a silicon atom andan oxygen atom, and the pores may be communicated with or independent ofone another.

First, a method for preparing the fine particles 3 having a large numberof open (communicated) pores will be described.

Such fine particles 3 can be prepared by crushing meso-porous silica ora zeolite crystal with regularity such as a honeycomb structure.Alternatively, the bake temperature (the hard bake temperature) employedin forming a porous film or a porous structure described in the first orsecond conventional example is increased to be higher than in the firstor second conventional example, so as to obtain a porous film or aporous structure in which the crosslinkage between silicon resins isreinforced, and this porous film or porous structure can be crushed togive the fine particles 3. Alternatively, colloidal silica, andspherical colloidal silica in particular, obtained through hydrolysis ofalkoxysilane, such as tetramethoxysilane or tetraethoxysilane, can beused as the fine particles 3.

Next, a method for preparing the fine particles 3 having a large numberof closed (independent) pores will be described.

Such fine particles can be prepared by crushing a porous film or aporous structure formed by using fine particles of an organic polymer asa porogen. Also in this case, the bake temperature employed in forming aporous film or a porous structure described in the first or secondconventional example is increased to be higher than in the first orsecond conventional example, so as to obtain a porous film or a porousstructure in which the crosslinkage between silicon resins isreinforced, and this porous film or porous structure can be crushed togive the fine particles 3. Alternatively, the fine particles 3 may havea structure in which colloidal silica, and spherical colloidal silica inparticular, is adhered around an organic polymer working as a nuclear.

In either case, the fine particle 3 preferably has a size more thanapproximately 1 nm and less than approximately 30 nm, and each pore ofthe fine particle 3 preferably has a size more than approximately 0.5 nmand less than approximately 3 nm.

The solvent 4 may be a solvent that is substantially completelyevaporated at the temperatures of the pre-bake and the soft bake, andexamples are alcohols such as methanol, ethanol and isopropyl alcohol;and organic solvents such as cyclohexane, NMP (N-methylpyrolidone),PGMEA (propylene glycol monomethyl ether acetate), PGME (propyleneglycol monomethyl ether) and PGMPE (propylene glycol monopropyl ether).

Embodiment 2

Embodiment 2 of the invention will now be described with reference toFIGS. 2A and 2B. In Embodiment 2, a material for forming an insulatingfilm with low dielectric constant is embodied as a fine particle.

FIG. 2A shows a porous structure 5 used for preparing fine particles 6,and FIG. 2B shows the fine particles 6 prepared by crushing the porousstructure 5.

The porous structure 5 has a plurality of open pores randomlydistributed therein, and the fine particles 6 each having a large numberof pores can be obtained by mechanically crushing the porous structure5. In order to mechanically crush the porous structure 5, the porousstructure 5 may be crushed through collision with a rapidly rotatingblade or the porous structure 5 contained in a sealed vessel is allowedto collide with the inner wall of the sealed vessel. When the fineparticles 6 are prepared in such a manner, the resultant fine particlesare in a variety of sizes, and therefore, the fine particles 6 arepreferably selected from these fine particles so as to be in a size morethan approximately 1 nm and less than approximately 30 nm.

As the porous structure 5, meso-porous silica or zeolite crystal withregularity such as a honeycomb structure can be used. Alternatively, thebake temperature (the hard bake temperature) employed in forming aporous film or a porous structure described in the first or secondconventional example is increased to be higher than in the first orsecond conventional example, so as to obtain a porous film or a porousstructure in which the crosslinkage between silicon resins isreinforced, and this porous film or porous structure may be used as theporous structure 5.

Each pore of the fine particle 6 preferably has a size more thanapproximately 0.5 nm and less than approximately 3 nm.

Embodiment 3

Embodiment 3 of the invention will now be described with reference toFIGS. 3A and 3B. In Embodiment 3, a material for forming an insulatingfilm with low dielectric constant is embodied as a fine particle 8.

FIG. 3A shows a porous structure 7 used for preparing fine particles 8and FIG. 3B shows the fine particles 8 prepared by crushing the porousstructure 7.

The porous structure 7 has a large number of closed pores substantiallyuniformly dispersed therein, and the fine particles 8 each having alarge number of pores can be obtained by mechanically crushing theporous structure 7. In order to mechanically crush the porous structure7, the porous structure 7 may be crushed through collision with arapidly rotating blade or the porous structure 7 contained in a sealedvessel is allowed to collide with the inner wall of the sealed vessel.When the fine particles 8 are prepared in such a manner, the resultantfine particles are in a variety of sizes, and therefore, the fineparticles 8 are preferably selected from these fine particles so as tobe in a size more than approximately 1 nm and less than approximately 30nm.

The porous structure 7 may be a porous film or a porous structure formedby using fine particles of an organic polymer as a porogen. Also in thiscase, when the bake temperature is set to be higher than that employedin the first or second conventional example, the resultant porousstructure 7 can attain large mechanical strength. Each pore of the fineparticle 8 preferably has a size more than approximately 0.5 nm and lessthan approximately 3 nm.

Embodiment 4

Embodiment 4 of the invention will now be described with reference toFIGS. 4A through 4C. In Embodiment 4, a material for forming aninsulating film with low dielectric constant is embodied as a fineparticle synthesized through a chemical reaction.

FIG. 4A shows a first fine particle 10A that is synthesized through achemical reaction and has a large number of pores. The first fineparticle 10A is a fine particle 9 a of colloidal silica, andparticularly spherical colloidal silica, produced through hydrolysis ofalkoxysilane such as tetramethoxysilane or tetraethoxysilane, and thefine particle 9 a has a large number of pores. The fine particle 9 a maybe a fine particle of meso-porous silica or zeolite crystal instead ofthe colloidal silica.

FIG. 4B shows a second fine particle 10B that is synthesized through achemical reaction and has a large number of pores. The second fineparticle 10B has a structure in which fine particles 9 a each having alarge number of pores are substantially uniformly adhered around anorganic polymer 10 a with a relatively small diameter. The fine particle9 a may be colloidal silica produced through the hydrolysis ofalkoxysilane such as tetramethoxysilane or tetraethoxysilane.Alternatively, the fine particle 9 a may be a fine particle ofmeso-porous silica or zeolite crystal instead of the colloidal silica.Furthermore, the fine particle 9 a and the organic polymer 10 a may bein a spherical or polyhedral shape.

FIG. 4C shows a third fine particle 10C that is synthesized through achemical reaction and has a large number of pores. The third fineparticle 10C has a structure in which fine particles 9 a each having alarge number of pores are substantially uniformly adhered around anorganic polymer 10 b with a relatively large diameter. The fine particle9 a may be colloidal silica produced through the hydrolysis ofalkoxysilane such as tetramethoxysilane or tetraethoxysilane.Alternatively, the fine particle 9 a may be a fine particle ofmeso-porous silica or zeolite crystal instead of the colloidal silica.

Furthermore, the fine particle 9 a and the organic polymer 10 b may bein a spherical or polyhedral shape. Moreover, the fine particles 9 a arepreferably adhered around the organic polymer 10 b not substantiallyuniformly but in special arrangement for increasing the mechanicalstrength of the third fine particle 10C.

The first, second or third fine particle 10A, 10B or 10C preferably hasa size more than approximately 1 nm and less than approximately 30 nm,and each pore of the fine particle 9 a preferably has a size more thanapproximately 0.5 nm and less than approximately 3 nm.

Embodiment 5

Embodiment 5 of the invention will now be described with reference toFIGS. 5A through 5E. In Embodiment 5, an insulating film with lowdielectric constant and a method for forming the same by using thesolution according to Embodiment 1 are embodied.

First, as shown in FIG. 5A, the solution according to Embodiment 1 isprepared.

Specifically, a solution including a silicon resin 2, fine particles 3described in any of Embodiments 2 through 4 and a solvent 4 is containedin a vessel 1. Then, a semiconductor wafer 12 is placed on a spindle 11connected to a rotation mechanism, and an appropriate amount of solution14 is dropped on the semiconductor wafer 12 from a solution supply tube13 connected to the vessel 1.

Then, as shown in FIG. 5B, the spindle 11 is rotated so as to rotate thesemiconductor wafer 12, and thus, the solution 14 is spread to form athin film 15.

Next, as shown in FIG. 5C, the semiconductor wafer 12 on which the thinfilm 15 has been formed is placed on a hot plate 16 and annealed forevaporating the solvent. This procedure is generally designated aspre-bake, and is performed at a temperature of approximately 100° C. forapproximately 1 through 3 minutes.

Thereafter, as shown in FIG. 5D, the semiconductor wafer 12 is placed ona hot plate 17 and annealed at a temperature of approximately 200° C.for approximately 1 through 3 minutes. This procedure is generallydesignated as soft bake.

Next, as shown in FIG. 5E, after placing the semiconductor wafer 12 inan electric furnace 18, the temperature of the electric furnace 18 isincreased to approximately 400° C. through 450° C., and then, annealingis performed at the highest set temperature for approximately 1 hour.This procedure is generally designated as hard bake, and when thisprocedure is completed, an insulating film with low dielectric constant15A including the silicon resin 2 and the fine particles 3 is formed onthe semiconductor wafer 12. The hard bake may be performed by using ahot plate. Also, annealing is preferably performed with a hot platebetween the soft bake and the hard bake at an intermediate temperaturebetween the temperatures of the soft bake and the hard bake forapproximately 1 through 3 minutes.

In Embodiment 5, the silicon resin 2 is substantially stabilized in itsstructure because a basic siloxane structure is almost formed during thesoft bake, and siloxane skeletons are crosslinked during the subsequenthard bake, so that the low dielectric insulating film 15A can be rigidand attain large mechanical strength. In other words, the silicon resins2 are bonded to one another during the soft bake and the fine particles3 each having a large number of pores and the silicon resin 2 are bondedto each other.

In this manner, the low dielectric insulating film 15A of Embodiment 5has a structure in which the silicon resin 2 and the fine particles 3having pores are rigidly bonded to each other. Accordingly, the lowdielectric insulating film 15A is a porous film with toughness and largemechanical strength as compared with a siloxane structure made from asilicon resin alone.

Embodiment 6

Embodiment 6 of the invention will now be described with reference toFIGS. 6A, 6B, 7A and 7B. Also in Embodiment 6, an insulating film withlow dielectric constant and a method for forming the same by using thesolution according to Embodiment 1 are embodied.

When an insulating film with low dielectric constant is formed by themethod described in Embodiment 5, the state in which the pores areformed in the low dielectric insulating film is varied depending uponthe molecular structure of the solvent. Specifically, in the case (1)where a solvent that is substantially completely evaporated through thepre-bake, such as alcohol, is used, substantially no pores other than alarge number of pores present within the fine particles is formed.However, in the case (2) where a solvent that is not completelyevaporated during the pre-bake but is completely evaporated during thesoft bake is used and the solvent is composed of straight chainmolecules or molecules with a structure approximate to a straight chain,open pores are likely to be formed in a portion corresponding to thesilicon resin in addition to a large number of pores present within thefine particles. In this manner, the state of pores formed in aninsulating film with low dielectric constant depends upon the kind ofsolvent. This will now be described with reference to FIGS. 6A and 6B.

FIG. 6A shows the cross-sectional structure of a first low dielectricinsulating film 21 formed on a semiconductor wafer 20, and the first lowdielectric insulating film 21 includes a silicon resin 21 having poresand fine particles 23 each having a large number of pores. In thedrawing, a white portion inside the silicon resin 21 corresponds to apore. In the first dielectric insulating film 21, there are a largenumber of pores present within the fine particles 23 and open poresformed in the silicon resin 21, and hence, the first dielectricinsulating film 21 is a porous film having open pores as a whole.

FIG. 6B shows the cross-sectional structure of a second low dielectricinsulating film 24 formed on a semiconductor wafer 20, and the secondlow dielectric insulating film 24 includes a silicon resin 24 having nopores and fine particles 23 each having a large number of pores. In thesecond low dielectric insulating film 24, there is no pore in thesilicon resin 24, and hence, the second low dielectric insulating film24 is a porous film having a large number of closed pores as a whole.

FIG. 7A shows a first state of the first low dielectric insulating film21 of FIG. 6A, and the first state is obtained by using a material forforming an insulating film with low dielectric constant in which theratio of the fine particles 23 in the solute is lower than approximately30 through 50 wt %. In the first state, a structure of the silicon resin22 is the majority, the fine particles 23 having pores are present inthis structure, and the structure of the silicon resin 22 is rigidlybonded to the fine particles 23 having pores. In the case where the fineparticles 23 with larger mechanical strength than the silicon resin 22are introduced into the structure of the silicon resin 22 as in thefirst state, the resultant film can attain much larger mechanicalstrength than a structure composed of the silicon resin 22 alone.

FIG. 7B shows a second state of the first low dielectric insulating film21 of FIG. 6A, and the second state is obtained by using a material forforming an insulating film with low dielectric constant in which theratio of the fine particles 23 in the solute is higher thanapproximately 30 through 50 wt %. In the second state, the fineparticles 23 having pores correspond to the main skeleton of the firstlow dielectric insulating film 21, and the adjacent fine particles 23are bonded to each other through a structure of the silicon resin 22. Inthe second state, the fine particles 23 with larger mechanical strengththan the silicon resin 22 are introduced into the structure of thesilicon resin 22 similarly to the first state. Therefore, the resultantfilm can attain much larger mechanical strength than the structurecomposed of the silicon resin 22 alone, and in addition, since the ratioof the fine particles 23 having pores is higher than in the first state,the low dielectric constant is further lowered.

As described so far, in the low dielectric insulating film according toEmbodiment 5 or 6, fine particles each having a large number of poresare introduced into a structure of a silicon resin, and therefore, thelow dielectric insulating film can be formed as a porous film having adielectric constant as low as approximately 2.5 or less and largemechanical strength. The mechanical strength of the low dielectricinsulating film according to Embodiment 5 or 6 is approximately 6 GPa ormore in the Young's modulus.

In other words, in the low dielectric insulating film of Embodiment 5 or6, the fine particles having a large number of pores and introduced forforming pores in the film do not disappear during the formation butremain in the resultant porous film and are strongly bonded to thestructure of the silicon resin. Therefore, when the ratio of the fineparticles having pores in the solution is increased to 30 wt % or moreso as to further lower the dielectric constant by increasing theporosity of the low dielectric insulating film, the mechanical strengthis not lowered differently from the case where a fullerene is used butrather increased.

When organic silicon in which silicon and an organic group such as amethyl group are bonded to each other or a silicon resin includingorganic silicon is used as the silicon resin, the dielectric constant ofthe resultant low dielectric insulating film can be further lowered.

Also, when an organic polymer such as a polymer formed through anaryl-ether bond or an aryl-aryl bond is used instead of the siliconresin, the dielectric constant of the resultant dielectric insulatingfilm can be further lowered. This is because MSQ in a bulk has adielectric constant of approximately 2.9 while the organic polymer in abulk has a dielectric constant as low as 2.6. Therefore, since thisrelationship holds also in a porous film in which a silicon resin and anorganic polymer have pores, the dielectric constant can be easilylowered by using an organic polymer instead of the silicon resin. Also,in the first state of the first low dielectric insulating film 21 shownin FIG. 7A, when a compound for reinforcing the bond between the siliconresin and the fine particles is additionally used, the mechanicalstrength can be further increased.

Furthermore, in the second state of the first low dielectric insulatingfilm 21 shown in FIG. 7B, when a compound for reinforcing the bondbetween the fine particles included in the silicon resin is additionallyused, the mechanical strength can be further increased.

An example of the compound for reinforcing the bond between the siliconresin and the fine particles is alkoxysilane. For example, two methylgroups (CH₃—) and two methoxy groups (CH₃O—) are bonded to silicon (Si)in dimethyldimethoxysilane, and therefore, the crosslinkage between thesilicon resin and the fine particles can be accelerated in the soft bakeand the hard bake performed in forming the film. Also, sincealkoxysilane can accelerate the crosslinkage between fine particles aswell as the crosslinkage between an organic polymer and fine particles,it can be suitably used as the compound for reinforcing the bond in thisinvention.

Embodiment 7

Embodiment 7 of the invention will now be described with reference toFIG. 8.

In Embodiment 7, a semiconductor device including an insulating filmwith low dielectric constant is embodied.

FIG. 8 shows the cross-sectional structure obtained in bonding a wire toa semiconductor device that has a multilayer interconnect structures forexample, a three-layered interconnect structure and uses the lowdielectric insulating film of Embodiment 5 or 6 as an insulating film.In FIG. 11, a reference numeral 30 denotes a semiconductor wafer, areference numeral 31 denotes an insulating film with low dielectricconstant, reference numerals 32, 34 and 36 are metal interconnects,reference numerals 33, 35, 36 and 38 denote via plugs, and a referencenumeral 39 denotes a pad to be connected to an external interconnect.The metal material for the metal interconnects 32, 34 and 36 may becopper or aluminum alloy. In using copper interconnects, copper can beused for the via plugs, and in using aluminum interconnects, tungstenmay be used for the via plugs.

As shown in FIG. 8, when a wire 40 is bonded to the top face of the pad39, the semiconductor device is mounted in a package not shown.

In Embodiment 7, since the low dielectric insulating film 31 has largermechanical strength than a conventional porous film, no cracks arecaused in the pad 39 and the metal interconnects 32, 34 and 36. Also,since the low dielectric insulating film 31 has large strength forholding the metal interconnects 32, 34 and 36, the resultantsemiconductor device can be stabilized.

1-37. (canceled)
 38. A material for forming a low dielectric constantfilm comprising, a solution including a resin, a solvent, and a fineparticle principally composed of a silicon atom and an oxygen atom, andwherein the fine particle includes a pore, and the fine particle has asize equal to or more than 1 nm and equal to or less than 30 nm.
 39. Thematerial for forming a low dielectric constant film of claim 38, whereinthe pore in the fine particle has a size equal to or more than 0.5 nmand equal to or less than 3 nm, and wherein the size of the fineparticle is bigger than the size of the pore.
 40. The material forforming a low dielectric constant film of claim 38, wherein a pluralityof pores in the fine particle are partially confined.
 41. The materialfor forming a low dielectric constant film of claim 38, wherein aplurality of pores in the fine particle are isolated.
 42. The materialfor forming a low dielectric constant film of claim 38, wherein theresin including a silicon is an organic silicon.
 43. The material forforming a low dielectric constant film of claim 38, wherein the resinincluding a silicon is the organic silicon having a bond between asilicon atom and a methyl group, or the organic polymer includes anaryl-ether bond or an aryl-aryl bond.
 44. The material for forming a lowdielectric constant film of claim 38, wherein the solution furtherincludes a compound for reinforcing a bond between the resin and thefine particle.
 45. The material for forming a low dielectric constantfilm of claim 38, wherein the fine particle has a crystal structure, orprincipally composed of a meso-porous silica or a zeolite crystal. 46.The material for forming a low dielectric constant film of claim 38,wherein a rate of the fine particle in a solute is higher than 30 wt %.47. A material for forming a low dielectric constant film comprising, asolution including a resin, a solvent, and a fine particle principallycomposed of a silicon atom and an oxygen atom, wherein the fine particleincludes a pore having a size equal to or more than 0.5 nm and equal toor less than 3 nm.
 48. The material for forming a low dielectricconstant film of claim 47, wherein a plurality of pores in the fineparticle an partially confined.
 49. The material for forming a lowdielectric constant film of claim 47, wherein a plurality of pores inthe fine particle are isolated.
 50. The material for forming a lowdielectric constant film of claim 47, wherein the resin includes asilicon or organic polymer.
 51. The material for forming a lowdielectric constant film of claim 47, wherein the resin including asilicon is an organic silicon.
 52. The material for forming a lowdielectric constant film of claim 51, wherein the organic siliconincludes a bond between a silicon atom and a methyl group, or theorganic polymer includes an aryl-ether bond or an aryl-aryl bond. 53.The material for forming a low dielectric constant film of claim 47,wherein the solution further includes a compound for reinforcing a bondbetween the resin and the fine particle.
 54. The material for fanning alow dielectric constant film of claim 47, wherein the fine particle hasa crystal structure, or principally composed of a meso-porous silica ora zeolite crystal.
 55. The material for forming a low dielectricconstant film of claim 47, wherein a rate of the fine particle in asolute is higher than 30 wt %.
 56. A material for forming a lowdielectric constant film comprising, a fine particle principallycomposed of a silicon atom and an oxygen atom, and wherein the fineparticle has a crystal structure or porous structure including a pore,and wherein the pore has a size equal to or more than 0.5 nm and equalto or less than 3 nm.
 57. The material for fanning a low dielectricconstant film of claim 56, wherein the fine particle has a size equal toor more than 1 nm and equal to or less than 30 nm, and wherein the sizeof the fine particle is bigger than the size of the pore.